Hydrophobic interaction chromatography (HIC) is used as a polishing step in many monoclonal antibody purification processes (Shukla and Thommes, Trends in Biotechnol 28(5): 253-261, 2010). This mode of chromatography is particularly useful for aggregate removal and also provides clearance of other process-related impurities such as host cell protein, leached Protein A and endogenous viruses (McCue et al., Bioprocess Biosys Eng 31: 261-275, 2008; Shukla et al., J Chromatogr A 848: 28-39, 2006; Jiang et al., Biotechnol Bioeng 107(6): 985-997, 2010). HIC is based on interactions between hydrophobic (aliphatic or aromatic) ligands on the stationary phase with hydrophobic patches on the surface of the proteins. Interactions of proteins with hydrophobic ligands are usually promoted by kosmotropic salts such as ammonium sulfate, sodium citrate, potassium phosphate and others (Melander et al., J Chromatogr A 317: 67-85, 1984). Kosmotropic salts interact with water molecules to reduce solvation of the protein molecules in solution and to expose their hydrophobic patches to promote binding (Liu et al., mAbs 2(5): 480-499, 2010). Elution is usually facilitated by decreasing salt concentration and sometimes by using organic mobile phase modifiers.